Analyses of vaccination protocols for Leptospira interrogans serovar autumnalis in hamsters.

Leptospirosis, caused by Leptospira spp., is a zoonotic disease found worldwide. Killed whole cell leptospiral vaccines have been used as effective vaccines to elicit specific antibodies for protection. However, the involvement of cytokine responses after vaccination is not well characterized. Hamsters were immunized with killed L. interrogans serovar Autumnalis before challenge to study cytokine mRNA expression levels (interferon [IFN]-gamma, tumor necrosis factor [TNF]-alpha, interleukin [IL]-10, and IL-4). Vaccinated groups showed 92-100% survival rates, whereas control hamsters died within 6-10 days. However, live organisms were detected in vaccinated groups, and mild to moderate pathology was observed early in infection. IFN-gamma and TNF-alpha mRNA expression levels correlated with the severity of infection and lung pathology, whereas IL-4 and IL-10 expression levels were significantly higher in vaccinated groups. In summary, commonly used vaccines changed the cytokine profiles and protected hamsters from death but failed to stimulate sterile immunity and were unable to prevent the occurrence of pathology.